HR: 16:45h
AN: T14A-04    [Abstracts]
TI: Evolution Of The West Antarctic Rift System And the Importance of Crustal Heat Production
AU: * Huerta, A D
EM: ahuerta@geosc.psu.edu
AF: The Pennsylvania State University, Dept. of Geosciences, University Park, PA 16802 United States
AU: Harry, D L
EM: dharry@cnr.colostate.edu
AF: Colorado State University, Dept. of Geosciences, Fort Collins, CO 80523 United States
AB: Two distinct stages of extension are recognized in the West Antarctic Rift system (WARS). During the first stage in the Late Cretaceous through middle Paleogene Periods extension was broadly distributed throughout most of the Ross Sea region. Later, during the Late Paleogene and younger, the style of extension changed and was focused primarily in the Terror Rift, near the boundary with the East Antarctic craton. We have developed a finite element model to study the processes and conditions responsible for this two-stage evolution of rifting. Model results consistent with the geologic history of the WARS indicate that the transition from a period of broadly distributed extension to a later period of strongly focused rifting can evolve naturally without requiring a change in either the regional stress regime or thermal state. No change in plate motion directions or rates or changes in the mantle thermal state (impingement of a plume) are required. The initial stage of modeled diffuse extension throughout West Antarctica results from a prescribed uniformly weak West Antarctic lithosphere (thinner, hotter) versus a prescribed stronger East Antarctic lithosphere (thicker, colder). The transition from diffuse to focused extension under constant regional stress and thermal conditions occurs only under a limited set of initial thermal conditions. Simulations that have an initial West Antarctic thermal structure with significant heat from the crust result in a lithosphere that strengthens as it thins. This strengthening is due to the cooling of the upper mantle as the thickness of the crust is reduced (thus the total heat generated in the crust is reduced). As a subset of this class of simulations, instances in which the initial East Antarctic crust generates moderately high amounts of heat result in a focusing of extension near the boundary between East and West Antarctica. This focusing is due to the relative weakness of the upper mantle near the East/West Antarctic boundary due to heat conducted from the warm East Antarctic crust. Thus, crustal heat production can play an important role in controlling the deformational evolution of extensional systems.
DE: 8109 Continental tectonics--extensional (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting